1. Technical Field
This invention relates to construction material. In greater detail, this invention relates to construction material reclaimed from ash from municipal waste combustors (MWC) traditionally disposed of by landfill, which can be used safely as roadbase material.
2. Prior Art
Of the waste arising from urban activity, refuse consisting chiefly of combustibles has been disposed of by incineration, the ash thereof deposited in landfills. In recent years, however, sites for landfill disposal of combustor ash have decreased, making disposal increasingly difficult. Thus, there have been plans to reuse useful components included in MWC ash, thereby reducing the volume of combustor ash disposed of in landfills, and to employ such ash as a resource.
For example, Japanese Patent Application Publication Sho 56-124481 proposes processing MWC ash by recovering metal from such ash, followed by comminuting with a comminutor, adding sintering auxiliary agent for blending and granulating, and sintering and solidifying the resulting granulated substance in a sintering furnace. However, enormous energy is required to sinter and solidify granulated substances in a sintering furnace, and this is not only contrary to the tide of energy conservation, but it results in solidified substances not price competitive with natural aggregate.
On the other hand, Japanese Patent Application Publication Hei 1-16555 proposes mixing an appropriate amount of pit soil with combustor ash, then mixing a suitable quantity of unslaked lime therein, to create reclaimed earth. However, in many cases there are minute quantities of lead, chromium and other hazardous heavy metals in the combustor ash, presenting dangers in use for landfill or housing lots when merely mixed with pit soil and unslaked lime.
In addition, Japanese Patent Application Publication Hei 7-96263 proposes treating waste combustor ash by comminuting such ash, producing particle substances with particle size distribution of 10 mm or less in particle diameter, adjusting moisture content therein to 10 to 15% in weight, adding cement bonding agent at a ratio of 10 to 15% in weight relative to particle substances, followed by mulling and pressure molding in a mold to create concrete blocks. However, this method requires cement bonding agent and the pressure molding process. Moreover, despite stabilization of heavy metals contained in the combustor ash through such means as insolubility by the strong alkalinity of the cement, adsorption on hydrate surfaces of cement minerals, intra-hydrate replacement of atoms or radicals with metallic ions, physical sealing by cement gels, etc., it cannot be denied that after much time there is a risk of heavy metal leaching, concrete cracking, concrete deterioration and heavy metal discharge. Consequently, there has been demand for the development of materials for the economic and safe recycling of useful substances from MWC ash.
As a result of research to solve the foregoing problem, it was discovered that construction material can be derived from sorting, separating and drying MWC ash, the particles having maximum particle diameter of 5-40 mm with wide particle distribution, and containing only small quantities of moisture and unburned substances, with heavy metal immobilization agent added, and being mulled, California Bearing Ration has a revised CBR of 20% or more, making it useful and safe for use in various kinds of roadbase materials.
In other words, this invention provides:
(1) Construction material characterized in that it is obtained from sorting, separating and drying municipal waste combustor ash, the particles having a maximum particle diameter of 5-40 mm, a U-coefficient of 10 or more, and ignition loss of 10% or less in weight, with heavy metal immobilization agent added, and being mulled; and
(2) The construction material set forth in paragraph (1), wherein the heavy metal immobilization agent is phosphoric acid and/or ferrous sulfate.
None of the methods of the prior art provide the desired end product.
In one aspect of the present invention there is provided construction material comprising granular material reclaimed from the ash of a municipal water combustor wherein the ash is subjected to sorting and separating recovered metals. The granular material includes particles having a maximum particle diameter of 5 to 40 mm, a U-coefficient of 10 or more, and an ignition loss of 10% or less in weight and is subjected to at least one heavy metal immobilization agent. Other aspects include the heavy metal immobilization agent being phosphoric acid. Also, the ash is further subjected to a second heavy metal immobilization agent consisting of ferrous sulfate. In another aspect of the invention the ash is subjected to both of two heavy metal immobilization agents comprising phosphoric acid and ferrous sulfate.
Additionally, the ash is further subjected to drying and also is further subjected to drying before subjecting the ash to at least one heavy metal immobilization agent. The ash is further subjected to mulling the material after subjecting the ash to at least one heavy metal immobilization agent. In another aspect of the invention steps are combined such that the ash is further subjected to drying before subjecting the ash to at least one heavy metal immobilization agent and further subjecting the ash to mulling after subjecting the ash to at least one heavy metal immobilization agent.
Finally, in another aspect of the invention the ash is sequentially subjected to (1) sorting according to particle size; (2) comminuting particles greater than 40 mm in size to a lesser size; (3) blending the particles of various sorted sizes to create a U-coefficient of 10 or greater; (4) drying; (5) at least one heavy metal immobilization agent; and (6) mulling. The ash is further subjected to a second heavy metal immobilization agent, wherein at least one heavy metal immobilization agent is phosphoric acid and another agent is ferrous sulfate. The granular material includes non-ferrous metals.